The use of sputtering in order to deposit coatings on substrates is known in the art. For example, and without limitation, see U.S. Pat. Nos. 5,922,176; 5,403,458; 5,317,006; 5,527,439; 5,591,314; 5,262,032; and 5,284,564, the entire contents of each of which are hereby incorporated herein by reference. Briefly, sputter coating is a thin film coating process that involves the transport of almost any material from a target to a substrate of almost any other material. The ejection of the target material is accomplished by bombarding the surface of the target with gas ions accelerated by a high voltage. Particles are ejected from the target as a result of momentum transfer between the accelerated gas ions and the target. Upon ejection, the target particles traverse the sputtering chamber and are subsequently deposited on a substrate as a thin film.
Sputtering processes typically utilize an enclosed chamber confining a sputtering gas, a target electrically connected to a cathode, a substrate, and a chamber which itself may serve as the electrical anode. A power supply typically is connected such that the negative terminal of the power supply is connected to the cathode and the positive terminal is connected to the chamber walls. In operation, a sputtering gas plasma is formed and maintained within the chamber near the surface of the sputtering target. By electrically connecting the target to the cathode of the sputtering power supply and creating a negative surface charge on the target, electrons are emitted from the target. These electrons collide with atoms of the sputtering gas, thereby stripping away electrons from the gas molecules and creating positively charged ions. The resulting collection of positively charged ions together with electrons and neutral atoms is referred to generally as a sputtering gas plasma. The positively charged ions are accelerated toward the target material by the electrical potential between the sputtering gas plasma and the target and bombard the surface of the target material. As ions bombard the target, molecules of target material are ejected from the target surface and coat the substrate.
One known technique for enhancing conventional sputtering processes involves arranging magnets behind or near the target to influence the path taken by electrons within the sputtering chamber, thereby increasing the frequency of collisions with sputtering gas atoms or molecules. Additional collisions create additional ions, thus further sustaining the sputtering gas plasma. An apparatus utilizing this enhanced form of sputtering by means of strategically located magnets generally is referred to as a magnetron system.
Unfortunately, conventional sputtering techniques suffer from several disadvantages. For example, stress asymmetry in the travel and cross-coated directions of sputter-deposited polycrystalline films is a concern, especially in large-area applications that often require film patterning. Such applications include, for example, photovoltaic applications, flat-panel (e.g., plasma, LCD, etc.) display applications, etc. Some of the negative effects of stress asymmetry include, for example, layer delamination after laser scribing and subsequent heating in connection with photovoltaic devices, the formation of “mottling” defects in low-emissivity (low-E) products, layer peeling, etc. In certain coating applications, the inventors of the instant application observed stress asymmetry amount to a factor of three. In other words, the stress in the cross-coater direction was approximately three times as great as the stress in the travel direction, as measured, for example, in MPa.
One of the causes of stress asymmetry relates to the significant oblique component of the incoming material flux. The oblique component is subject to “shadowing effects,” e.g., whereby crystalline tips (e.g., “higher points”) receive more deposited material per unit time than valleys. Such shadowing effects tend to result in the formation of a granular structure including voids, which contributes to an increase in tensile stress in the direction of the higher oblique components, and/or a reduced amount of compressive stress, depending on the film. In this regard, FIG. 1 is an enlarged view of a sputter coated film produced using a conventional sputtering apparatus. FIG. 1 shows “normal” growth that tends to result in substantially columnar crystalline growth, as well as oblique growth that tends to result in voids.
It noted that the same or similar causes also contribute to “edge effects,” e.g., where the thickness and sometimes even the physical properties of the coating are different from those of the rest of the coated area.
Thus, it will be appreciated that there is a need in the art for improved sputtering apparatuses and/or methods. It also will be appreciated that there is a need in the art for sputtering apparatuses and/or methods that reduce stress asymmetry in polycrystalline films.
One illustrative aspect of certain example embodiments relates to sputtering apparatuses that include one or more substantially vertical, non-conductive shield(s) are provided, with such shield(s) helping to reduce the oblique component of sputter material flux and also promoting the growth of more symmetrical crystallites.
In certain example embodiments of this invention, a magnetron sputtering apparatus for sputter coating an article in a reactive environment is provided. A vacuum chamber is provided. A sputtering target is located in the vacuum chamber, with the sputtering target having a target material located thereon. At least one shield is located proximate to the target such that a major axis of the each said shield runs parallel to a travel direction of the article to be sputter coated. Each said shield is electrical isolated and substantially non-magnetic. Each said shield is disposed in the vacuum chamber at a location suitable for reducing the oblique component of sputter material flux produced during the sputter coating of the article.
In certain example embodiments, a method of making a coated article is provided. A coating is sputtered onto the article via a magnetron sputtering apparatus comprising a vacuum chamber and a sputtering target located in the vacuum chamber, with the sputtering target having a target material located thereon, and with at least one shield located proximate to the target such that a major axis of the shield runs parallel to a travel direction of the article to be sputter coated. Each said shield is electrical isolated and substantially non-magnetic. Each said shield is disposed in the vacuum chamber at a location suitable for reducing the oblique component of sputter material flux produced during the sputter coating of the article such that the difference between the travel direction tensile stress and the cross-coater tensile stress of the coating on the article is less than about 15%.
In certain example embodiments, a magnetron sputtering apparatus for sputter coating an article in a reactive environment is provided. A vacuum chamber is provided. A sputtering target is located in the vacuum chamber, with the sputtering target having a target material located thereon. A cathode is connected to the planar sputtering target. One or more magnets are arranged to facilitate the sputter coating of the article. A plurality of shields is located proximate to, and spaced apart from, the target such that a major axis of each said shield runs parallel to a travel direction of the article to be sputter coated. Each said shield is electrical isolated and substantially non-magnetic. The length of each said shield is substantially the same as the dimension of the target that corresponds to the travel direction of the article to be sputter coated. Each said shield is disposed in the vacuum chamber at a location suitable for reducing the oblique component of sputter material flux produced during the sputter coating of the article.
The features, aspects, advantages, and example embodiments described herein may be combined to realize yet further embodiments.